The invention relates to a method for producing a fastening assembly comprising a series of layers and a screw, the screw comprising a screw head equipped with a driving point, a shaft extending into a displacement tip, a thread extending into the displacement tip and an unthreaded shaft portion arranged between the thread and the screw head.
Furthermore, the invention relates to a fastening assembly and to a screw for such a fastening assembly.
The method, fastening assemblies and screws described here are usually used for fastening the outer and inner metal sheets of sandwich panels. Here, the series of metal sheets is intended to be held together by fasteners, which are cost-effective and can be inserted easily and rapidly during use.
All of the conventional prior-art solutions provide for boring the metal sheets that are to be connected, whether this is carried out by pilot-boring using a conventional drill or by using a screw having a boring tip. If pilot boring is carried out using a conventional drill, riveting or screwing can be carried out subsequently. If the fastener is a screw, then reverse locking should always be provided, which prevents the fasteners from being lost from the fastening assembly, in particular due to external influences such as vibrations or the like. For this purpose, an unthreaded shaft portion is conventionally used in that it is possible for the thread to simply end before reaching the screw head.
If a fastener that is inserted into a pilot hole is not selected as a fastener for the fastening assembly but instead a fastener having a displacement tip is selected, then it is no longer practical to use a thread that ends axially in a point. Here, according to the prior art, double threads have to be used in order to ensure the required reverse locking. However, double threads are comparatively complex and expensive to produce.
Screws that have a thread which extends into the tip are known in particular as wood screws. It is likewise known to equip such screws with an unthreaded portion between the head and the end of the thread. For example, such a screw is described in DE 202 11 445 U1.